Lost circulation is a complex downhole situation in which the working fluid leaks into the formation in drilling engineering, and is one of the most common and frequently encountered complex problems in drilling operations. Lost circulation is always a problem of great concern in the petroleum industry in China and foreign countries, because the complex downhole situations incurred by lost circulation are very harmful to well drilling and completion work. Once lost circulation occurs in drilling operations, it not only causes delayed drilling, loss of the drilling fluid, and damages to the oil and gas reservoir, and hinders the normal operation of geological logging, but also may cause wellbore instability and consequently result in a series of complex situations and accidents, such as well collapse, jamming of drilling tools, and well blowout, etc. If improperly handled, it may even result in abandonment of the well and severe economic losses. It is very important to handle lost circulation timely and maintain normal drilling. Therefore, it is highly necessary to develop new plugging agents.
Plugging materials are indispensable materials in the leak prevention and plugging process in drilling engineering.
Among the plugging materials, the most widely used water-absorbing polymer is hydrolyzed polyacrylamide (HPAM), but HPAM may cause pumping difficulties and affect the performance of the drilling fluid when it is used in plugging operation because its water absorption rate is too high. Consequently, a part of the plugging agent can't enter into the leakage zone and thereby causes a compromised plugging effect because its particle size is too large. In some large fractures and high-permeability formations, the strength of the water-absorbent resin can't meet the plugging requirement. Hence, it is not ideal to solely use a polymer gel system for plugging operation.
Among the plugging materials, chemical plugging materials mainly refer to plugging agents that mainly consist of polymers. Chemical plugging materials may be generally categorized into gels, resins, and expandable polymers, wherein, the expandable polymers mainly include SYZ expandable plugging agents, polyurethane foam expandable plugging agents and TP-9010. These three kinds of expandable polymers absorb water and expand after they enter into a leakage zone, and thereby plug up the leakage zone. However, they absorb hydrocarbons while absorbing water.
Therefore, it is of great significance to study and develop water-absorbing and hydrocarbon-resistant polymers for leak plugging.